export function demo1() {
  let h1 = document.createElement('h1');
  h1.innerText = "Hello ~~"
  document.body.append(h1);
  document.body.style.backgroundColor = '#ddd';
}

export function demo2() {
  let div = document.createElement('div');
  document.body.append(div);
  setInterval(() => { div.innerText = (new Date).toLocaleTimeString(); }, 1000);
}